Hydraulic Jumps in Turbidity Currents

Abstract

If uniform flow conditions are approached, turbidity currents should be supercritical (Froude number greater than unity) while passing through submarine canyons, and subcritical (Froude number less than unity) in the upper submarine fan channel. The change in flow regime requires that the current pass through a hydraulic jump in the vicinity of the canyon mouth. During the jump, the velocity of the flow would be reduced and its thickness markedly increased. The aspects of such hydraulic jumps are examined. The quantitative analysis of hydraulic jumps in turbidity currents is based upon solutions of the momentum flux equation and the equation resulting from the assumption of a continuity of sediment flux. It is found that for the average submarine canyon-channel system, the flow would more than double in thickness and its velocity would be halved during a hydraulic jump. The entrainment of water through the interface of the flow during the jump is significant in reducing the density of the current. The higher the initial Froude number, the greater the expected density reduction. However, the density reduction due to the jump is probably not sufficient to convert a high-density slide into a low-density turbidity current. There must be an initial density reduction by entrainment while the slide is passing through the canyon at high Froude number. Turbulence generated within the hydraulic jump would stir the flow and help to insure suspension of its sediment.